The present invention relates generally to an operating device having an operating knob for the setting of an exposure factor, which device is provided on a camera attachment which is removably connected to a camera body, with the knob being coupled with an exposure factor setting or adjusting mechanism in the camera body; more particularly, the present invention relates to a mechanism for locking the knob at one or more predetermined positions thereof.
Besides the known film sensitivity setting device for a view finder unit or a shutter speed setting device for a built-on type exposure meter, a typical example of the above-mentioned operating device is a shutter speed setting device located on a view finder unit having a pentagonal prism and removably connected to a single lens reflex camera. In accordance with the operation of such a shutter speed setting device, after the view finder unit has been attached to the camera body, the operating knob thereof is manually moved to a position where it is coupled with a shutter speed setting or adjusting mechanism in the camera.
As for the shutter speed setting device of this type in which the operating knob can be set to both automatic and manual exposure positions, a locking mechanism is well known which locks the operating knob at its automatic exposure position so that the knob may not be moved inadvertently to any manual exposure position to cause an unexpected exposure. However, as the locking mechanism is constructed so as to operate whenever the knob is moved to its automatic exposure position, such device suffers from the following inconveniences or drawbacks:
(a) When the view finder unit is attached to the camera body with the operating knob set to its automatic exposure position, the operating knob cannot be moved to the position where the device is coupled with the setting or adjusting mechanism unless the operating knob is released from the locking mechanism by a manipulation of a release member. However, such a manipulation has been found troublesome. PA1 (b) When the operating knob is moved so that it passes through its automatic exposure position, the locking mechanism locks the operating knob as soon as the latter reaches its automatic position. Accordingly, such troublesome manipulation is likewise necessary. PA1 (c) In the (b) situation, the operator may possibly regard the locking as a signal that the coupling between the operating knob and the shutter speed setting or adjusting mechanism in the camera body is accomplished. At this time an unexpected exposure will be effected if the shutter is released.